Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $91.55   12.811%   $103.2785   $103.28   $103.30   $103.30  
  Purchase #2 $62.99   9.294%   $68.8443   $68.84   $68.85   $68.80  
  Purchase #3 $202.75   11.595%   $226.2589   $226.26   $226.25   $226.30  
  Purchase #4 $217.29   6.102%   $230.549   $230.55   $230.55   $230.50  
  Purchase #5 $76.90   13.334%   $87.1538   $87.15   $87.15   $87.20  
  Purchase #6 $84.26   4.454%   $88.0129   $88.01   $88.00   $88.00  
  Purchase #7 $185.45   11.411%   $206.6117   $206.61   $206.60   $206.60  
  7 purchase totals = $921.19       $1,010.7091   $1,010.70   $1,010.70   $1,010.70